In Japan, the average span of human life has been increased and correspondingly patients suffering from diseases accompanied by a lowering of cerebral functions such as dementia, mental disorder, neurosis or the like associated with after-effects of cerebral infarction, cerebral arterial sclerosis or the like have been rapidly increased. This has become a serious social problem.
There have been compelling demands for the development of a medicine which shows excellent effect of treating or improving these diseases accompanied by the lowering of cerebral functions, but there has not yet been proposed any medicine exhibiting a satisfied effect for these diseases.
On the other hand, Japanese Patent Unexamined Publication (hereinafter referred to as "J.P. KOKAI") No. Sho 62-123181 discloses that a derivative of 2-phenyl-3-oxo-2H-1,4-benzothiazine represented by the following general formula (I) exhibits a platelet aggregation inhibiting effect and calcium antagonism and is useful as an agent for treating circulatory diseases, but does not disclose or suggest, at all, that the derivative be effective as a nootropic agent.